“Safety specification for elevator manufacture and installation (GB7588-2003)” describes the balance coefficient as follows: it is ratio of the total mass of the rated load and car to balancing weight.
“Lift-testing method (GB/T10059-2009)” and “Regulation for Lift Supervisory Inspection and Periodical Inspection—Traction and Positive Drive Lift (TSG T7001-2009)” set forth the detection method for elevator balance coefficient as follows: the car moves up and down at its full running range with a load of 30%, 40%, 45%, 50% and 60% of its rated load respectively; when the car and its counterweight move to a same horizontal location, the inputted current value of a motor is recorded; after that, current-load curve is plotted to identify the intersection point between the curve of upward movement and downward movement as the balance coefficient.
The above detection method, in which the load is increasingly added to the elevator in certain order, motor current value is recorded, and curve of current-load is plotted to determine the balance coefficient, has the advantage of being practiced using a general detection equipment and relevant detection technique is reliable and disadvantage of time consuming. For example, working time in field usually excesses 1 hour and it is approximately one-third of the total supervisory inspection time of the entire elevator.
As aforementioned prior art elevator balance coefficient detection method is time consuming and tedious, in recent years free-loaded balance coefficient detection technique has been developed eventually and some good effects have been brought by this new detection method. Examples of these new techniques include detection apparatus which is made by Anhui special equipment Inspection institute and in which balance coefficient is determined by detecting tension force of the steel rope located at two sides of the traction wheel, static lateral weight difference detection method and device developed by Liaoning Shihua University, and ADIASYSTEM elevator detection system created by TüV company, Germany. In these techniques there is no load and accordingly, there is no need to repeatedly move test weight. Till now, the problem remains that it employs a force detection device for detection of self weight of the elevator car and counterweight for data collection purpose. As a result, in site installation and detection is inconvenient. In addition, as data collection is performed for elevator static working condition, this is different from dynamic detection result based on Specifications GB/T10059-2009 and TSG T7001-2009. Therefore, use of them is quite limited.
A Chinese patent which publication No. is CN101670965A and issued on Mar. 11, 2010 discloses an elevator balance coefficient detection method. According to this method, upward movement torque Tup and downward movement torque Tdown of the motor running at a constant speed and with free of load is tested and, balance coefficient is achieved using formula (Tup+Tdown)*i/R/Q/2, wherein i is traction ratio, R is radius of the traction wheel, while Q is rated load. One drawback of this detection method lies in more than 20% of error is observed in its detection result which is confirmed by theory analysis and practical experience. The reason is when transmitting the elevator load to the motor, different transmission mechanism therein results in different transmission efficiency; and in addition, power transmission efficiency may be dramatically different for frontward direction (downward movement without load, and the elevator load being driven by mechanical construction of the motor) and backward direction (upward movement without load, and the elevator load driving the motor by the mechanical construction). For instance, widely used worm-gear traction machine has a frontward transmission efficiency of about 60%-80% and backward transmission efficiency of about 0%-40%. This detection method has not considered influence of the transmission efficiency upon detection results. Another drawback lines in detection accuracy of the motor torque as realized completely by motor torque detection function of the inverter cannot meet requirement as set forth in “Lift-testing method” (GB/T10059-2009).